1. Field of the Invention
The present invention relates to a switch for an electric power tool equipped with a trigger switch and, more particularly, to a switch for an electric power tool which includes an internal switch mechanism having an improved contact structure.
2. Prior Art
The prior art switch for an electric power tool has a trigger lever 100 and a movable contact plate 104 as shown in FIG. 8A The lever 100 has a trigger button 101 at its one end. A spring-biased slider 102 is mounted at the other end. The movable contact plate 104 makes a seesaw motion about a small support member 103. A movable contact 104a is mounted at the front end of the movable contact plate 104 and can be brought into and out of contact with a fixed contact 106 located opposite to the movable contact 104a. The movable contact plate 104 has a sliding surface 104b warped upward. When the trigger button 101 is pulled in, the slider 102 slides on the sliding surface 104b and passes beyond the support member 103, at which point the slider begins to move toward the fixed contact 105. If the slider moves further toward the movable contact 104a, the slider swings. As a result, the movable contact 104a at the front end comes into contact with the fixed contact 105 (see FIGS. 8B and 8C).
As shown in FIG. 8D, if the trigger button 101 is further pulled in, the slider 102 further moves on the sliding surface 104b toward the movable contact 104a. This further stabilizes the pressure contact of the movable contact 104a with the fixed contact 105. This is a so-called full stroke condition. In this state, electric power supplied to the motor can be maximized in a state of switching on of the power supply circuit When the trigger button 101 is ceased to be pulled in, the trigger lever 100 moves in the reverse direction, separating the contacts from each other. As a result, the initial state shown in FIG. 8A is regained.
However, the prior art trigger switch described above has the following problem. The slider 102 sliding on the upper surface of the movable contact plate 104 making a seesaw motion is made of a plastic. That is, the slider 102 is a resinous push member. As the sliding motion is repeated, the slider wears down, reducing the pressure of contact. This results in troubles including adhesion. Consequently, it has been impossible to maintain the pressure of contact constant.